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THE PHOTOGRAPHIC NEWS. Vol. XXVII. No. 1316.—Novemler 23, 1883. CONTENTS. PAGE Use of the Dynamo Machine in the Heliographic Department of the Vienna National Bank 737 The Mounting of Prints' 738 Gelatino-Bromide Paper for Positive Pictures 738 Photo-Block Printing from Nature 739 Coloured Photographs on Glass 740 “ By-tbe-Bye "—How to Make and Use a Velvet Roller *41 Review 742 Photo-Lithography and Photo-Zincography. By Major J. Waterhouse, B.S.C 742 Notes 743 PAGE Patent Intelligence 745 A Cheap and Efficient Exposer. By T. G. Whaite 747 Eosine and other Stained Plates. By Fred E. Ives 747 Glasgow Exhibition 747 Manchester Photographic Society : Past, Present, and Future 747 The Autotype or Carbon Process. By J. Pike 748 Correspondence 749 Proceedings of Societies 750 Talk in the Studio 751 To Correspondents 752 The Photographic News Registry 752 USE OF THE DYNAMO MACHINE IN THE HELIO- GRAPHIC DEPARTMENT OB' THE VIENNA NATIONAL BANK. Wb recently called attention to the way in which the gal vanic battery is employed by M. Scamoni to produce relief plates for photo-mechanical printing, and detailed the work pursued at the St. Peters burgh State Paper Office. We now take the opportunity of speaking of a similar application of electricity to the production of heliographic printing blocks at the National Bank of Vienna. Here, not a galvanic battery, but the well-known dynamo machine, which, as our readers know, is universally em ployed for the grinding out of electric light, is made use of. Many large establishments are now in possession of a dynamo-machine, so that its employment is adopted for electrotyping for more reasons than one. At the National Bank of Vienna, where, as in our Bank of England, the paper money of the country is printed, they make con siderable use of photography, especially in the case of fine and microscopical work. It is in the process of converting the photographic negative into a printing block that an electric current is desirable, and we may here remark that the Pretsch method of securing a gelatine relief, which we recently described in these columns, is the processin vogue at the Bank of Vienna. To secure an impression of the gelatine relief in metal by electrotyping, the dynamo- machine is brought into play. In employing the machine, however, it does not do, as in electric lighting, to produce an alternating current; that is to say, it does not answer to produce alternately, in rapid succession, currents of positive and negative electricity. If this were done, the fine copper particles would be dissolved as soon as they were deposited. Again, the dynamo machine should be of that order that gives quantity rather than electricity of high tension, and for this reason it should be put together in such a way that it has small internal resistance, Our sketch shows a dynamo of the nature required, which is from a factory of Messrs. Siemens and Halske, and which has a resistance only of 0-007ohm. In order to construct a machine with this minimum of resistance, the magnets are not surrounded with wires, but with thick copper bars, as shown in our sketch. The inductor-cylinder is in similar fashion fitted with thick copper rods. All copper portions of the machine, we may remark, become very hot from the powerful current generated. In the Bank of Vienna, this dynamo is not only employed for producing the copper electrotypes, but also for coating these with steel, or rather iron. This steel-plating is performed in a very simple fashion, If the copper surface